Let (1, 2) the focus of an ellipse and a straight line be known, and find the straight line equation!

solve

Let (x, y) be one focus of an ellipse and a straight line, and the other focus be (2-x, 4-y).

Substitute (x, y) and (2-x, 4-y) into the elliptic equation to get (1) and (2) respectively. Subtract these two equations to get a linear equation. It's a little hard to understand, to find a linear equation is to find the linear relationship between X and Y.